1. Field of the Invention
The present invention relates to a dust seal of a linear guide apparatus, and in particular, to an improvement in the assembling structure of an under seal in a linear guide apparatus.
2. Description of the Prior Art
Generally, a prior art linear guide apparatus, as shown in FIGS. 7 and 8, includes an axially extending guide rail 1 and a slider 2 movably straddling the guide rail 1. The guide rail 1 has ball rolling grooves 3 formed in both lateral sides in the axial direction, and the slider 2 has ball rolling grooves (not shown) formed in inner surfaces of both side walls 4 of a slider main body 2A so that the ball rolling grooves of the slider main body 2A respectively correspond to the ball rolling grooves 3 of the guide rail 1. Many balls are mounted rollably between opposing ball rolling grooves of the guide rail 1 and the slider main body 2A and the slider 2 moves on the guide rail 1 in the axial direction through the rolling of the balls. With this movement, it is necessary to continuously circulate the balls interposed between the guide rail 1 and the slider 2. To this end, a ball return path (not shown) is formed in each of the side walls 4 of the slider main body 2A penetrating axially and end caps 5 are provided at opposite ends of the slider main body 2A. A pair of curved paths each having a half-doughnut shape are formed in each of the end caps 5 so that the curved paths are in communication with the ball return paths respectively thereby to form ball infinitely circulating paths. However, dust or dirt particles are apt to be deposited on an upper surface la and on the ball rolling grooves 3 at lateral sides lb of the guide rail 1. When the dust or dirt particles are left as they are, the smooth rolling balls in the slider 2 will be disturbed, and in turn, will degrade the travelling accuracy and the stopping position accuracy of the slider 2.
Accordingly, in order to prevent the intrusion of the dust into the slider 2, dust seals are provided to close gaps between the slider 2 and the guide rail 1.
The dust seals at each side of the linear guide apparatus include a side seal 6 and an under seal 7. The side seal 6 is composed of a core metallic plate of a substantially inverted U-shape, and a rubber member secured on the core metallic plate. The side seal 6 is attached to the outer side of the end cap 5 of the slider 2 so that lip portions formed at inner edge of the side seal 6 slide on the upper surface 1a and the side surfaces 1b of the guide rail 1 to seal the gaps at each axial end of the slider 2. The under seal 7 is a long plate made of rubber and is attached by rivets to a lower surface of each of the side walls 4 of the slider 2 so that a lip portion formed at the inner edge of the under seal 7 slides on the lateral side surface 1b of the guide rail 1.
In such a prior art dust seal in a linear guide apparatus, it is desirable to adjust the interference or surplus of the lip portions of the seal for tight contact depending on the environmental conditions including the shape, size and the amount of the dirt particles deposited on the surfaces of the guide rail, or the working conditions of the dust seal per se including the non-uniformity in dimensions of components of the dust seal and including the hardness, or the limit in wear during use and the sliding resistance of the lip portion.
However, in the prior art assembling structure of the under seal 7, the under seal 7 is secured directly to the flat lower surface of the slider main body 2A by the rivets 8. As a result the following problems have been encountered. (1) Once the under seal has been secured by the rivets, the adjustment of the interference becomes impossible, and when the interference is not proper, the under seal which has been assembled must be removed. However, since the under seal is damaged at the time of removing, the under seal once assembled must be disposed of. Thus, the part cost is increased. (2) The working cost for boring rivet holes in the slider main body 2A is required. (3) Man-hours are required for rivet driving work at the time of assembling the under seal and for rivet removing work in replacing the under seal. (4) Since the under seal is secured by the rivets, when the rivets are driven strongly, the under seal will be flattened or compressed excessively by the rivets. As a result, the end and intermediate portions of the under seal will be deformed into a wave shape, and gaps tend to be formed. Therefore, the sealing function will be degraded before the under seal is worn. (5) Since the under seal and the heads of the rivets are protruded downwardly from the lower surface of the slider, a superfluous attaching space is necessary. Moreover, the protruded under seal or the rivet heads may collide with other members, causing the under seal to deform or fall away.